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Regression when using indexed type depending on function argument as return type #31672

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Regression when using indexed type depending on function argument as return type#31672
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Working as IntendedThe behavior described is the intended behavior; this is not a bugThe behavior described is the intended behavior; this is not a bug
@AlCalzone

Description

@AlCalzone
AlCalzone
opened on May 30, 2019
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TypeScript Version: 3.5.1

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Code

interface Foo {
	prop1: { value: number }[];
	prop2: string[];
}
function getFoo<T extends keyof Foo>(key: T): Foo[T] | undefined {
	if (key === "prop1") {
		return [{ value: 1 }]; // Error here
	}
}
const bar = getFoo("prop1"); // has correct type

Expected behavior:
No error. This used to work in 3.4.5

Actual behavior:

Type '{ value: number; }[]' is not assignable to type 'Foo[T]'.
  Type '{ value: number; }[]' is not assignable to type '{ value: number; }[] & string[]'.
    Type '{ value: number; }[]' is not assignable to type 'string[]'.
      Type '{ value: number; }' is not assignable to type 'string'.
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    Working as IntendedThe behavior described is the intended behavior; this is not a bugThe behavior described is the intended behavior; this is not a bug

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